Extracts of the medical mushroom Trametes versicolor (Tv) are prescribed as adjunctive immune therapy for women with breast cancer in both Asia and by licensed N. American naturopathic physicians. Japanese data suggest that Tv may improve survival and reduce recurrence in early stage breast cancer. While Tv is prescribed by NDs and other CAM practitioners and used with growing frequency among breast cancer patients as an over-the-counter supplement there have yet to be well-designed clinical studies in the U.S. Standardized commercially available products are in wide use. The proposed phase I/II clinical trial of orally administered Tv will be the first U.S. trial of this promising CAM adjunctive immunomodulatory cancer therapy. Primary Aims: 1) To conduct an observational study (n=22) with estrogen receptor negative Stage I and Ila breast cancer patients in order to monitor and quantify the natural course of immune recovery and adverse events, as well as changes in fatigue and QOL scores, during the six weeks immediately following the completion of radiation therapy. 2) To determine the safety and tolerability of orally administered capsules of standardized Tv using a modified Fibonacci dose-escalation design (n=24) with doses ranging from 3000 mg - 12,000 mg/day. The goal of the phase I trial is to determine the maximally tolerated dose. Secondary Aims: 3) To gather preliminary data that compare baseline and post-treatment immunologic measures in up to a maximum of four Tv dose cohorts depending on the MTD: 3000 mg, 6000 mg, 9000 mg, and 12,000 rag/day oral doses of encapsulated standardized Tv. End points include white blood cells (WBC), natural killer cell activity, macrophage phagocytic index, and peripheral blood mononuclear cell production of levels of interferon gamma and turrior necrosis factor-alpha. 4) To determine the feasibility of measuring changes infatigue and quality of life changes associated with Tv administration in women with Stage I or Ila breast cancer who have recently completed chemotherapy and radiation therapy. Breast cancer patients will be recruited from two cities, Seattle and Minneapolis. Study subjects will be screened and evaluated at the Bastyr University's Center for Natural Health in Seattle and the University of Minnesota's General Clinical Research Center. Each site will be responsible for recruiting and evaluating 23 patients each. All clinical data will be sent to the Center's Clinical Data Core located at Bastyr for data entry and analysis. These preliminary data will assist the Center in estimating effect sizes for later randomized efficacy trials of Tv in breast cancer patients.